'\" et
.TH sys_sem.h "0P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
sys/sem.h
\(em XSI semaphore facility
.SH SYNOPSIS
.LP
.nf
#include <sys/sem.h>
.fi
.SH DESCRIPTION
The
.IR <sys/sem.h> 
header shall define the following symbolic constant for use as a
semaphore operation flag:
.IP SEM_UNDO 12
Set up adjust on exit entry.
.P
The
.IR <sys/sem.h> 
header shall define the following symbolic constants for use as
commands for the
\fIsemctl\fR()
function:
.IP GETNCNT 12
Get
.IR semncnt .
.IP GETPID 12
Get
.IR sempid .
.IP GETVAL 12
Get
.IR semval .
.IP GETALL 12
Get all cases of
.IR semval .
.IP GETZCNT 12
Get
.IR semzcnt .
.IP SETVAL 12
Set
.IR semval .
.IP SETALL 12
Set all cases of
.IR semval .
.P
The
.IR <sys/sem.h> 
header shall define the
.BR semid_ds
structure, which shall include the following members:
.sp
.RS 4
.nf

struct ipc_perm  sem_perm  \fROperation permission structure.\fR
unsigned short   sem_nsems \fRNumber of semaphores in set.\fR
time_t           sem_otime \fRLast \fIsemop\fP\^(\|) time.\fR
time_t           sem_ctime \fRLast time changed by \fIsemctl\fP\^(\|).\fR
.fi
.P
.RE
.P
The
.IR <sys/sem.h> 
header shall define the
.BR pid_t ,
.BR size_t ,
and
.BR time_t
types as described in
.IR <sys/types.h> .
.P
A semaphore shall be represented by an anonymous structure,
which shall include the following members:
.sp
.RS 4
.nf

unsigned short  semval   \fRSemaphore value.\fR
pid_t           sempid   \fRProcess ID of last operation.\fR
unsigned short  semncnt  \fRNumber of processes waiting for \fIsemval\fR
                         \fRto become greater than current value.\fR
unsigned short  semzcnt  \fRNumber of processes waiting for \fIsemval\fR
                         \fRto become 0.\fR
.fi
.P
.RE
.P
The
.IR <sys/sem.h> 
header shall define the
.BR sembuf
structure, which shall include the following members:
.sp
.RS 4
.nf

unsigned short  sem_num   \fRSemaphore number.\fR
short           sem_op    \fRSemaphore operation.\fR
short           sem_flg   \fROperation flags.\fR
.fi
.P
.RE
.P
The following shall be declared as functions and may also be defined as
macros. Function prototypes shall be provided.
.sp
.RS 4
.nf

int   semctl(int, int, int, ...);
int   semget(key_t, int, int);
int   semop(int, struct sembuf *, size_t);
.fi
.P
.RE
.P
In addition, the
.IR <sys/sem.h> 
header shall include the
.IR <sys/ipc.h> 
header.
.LP
.IR "The following sections are informative."
.SH "APPLICATION USAGE"
None.
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fB<sys_ipc.h>\fP",
.IR "\fB<sys_types.h>\fP"
.P
The System Interfaces volume of POSIX.1\(hy2017,
.IR "\fIsemctl\fR\^(\|)",
.IR "\fIsemget\fR\^(\|)",
.IR "\fIsemop\fR\^(\|)"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
